Cosmic structure formation theory has passed test after test, predicting how many galaxies will form, where they will form, and what type of galaxy they will be. But for almost 20 years, its predictions about the central mass of dwarf galaxies have been wrong.

“Potentially, this is a very big problem for the model,” said Fabio Governato, a researcher at the University of Washington in Seattle. “It might imply that the dark matter particle that we think is the correct one is not the correct one, or maybe that gravity works differently than we think it does. So this is a very fundamental problem for physics.”

Multiprocessor machines may be increasingly common, but software designed to run in parallel is another story entirely. In this column, Darin Ohashi takes us back to basics to explain why programming in parallel is a whole different ball game.